Modified Pre-Fluxing Method For Energization of Single-Phase Transformers

Inrush current is the high-magnitude current that flows into power transformers upon energization. The severity of this current depends on transformer remnant flux, power system impedance, and voltage phase angle at the energization instant. Aimed at mitigating inrush current, this paper proposes a modified pre-fluxing method (MPFM) for the energization of single-phase transformers. This is to adjust the remnant flux of the core to its maximum feasible value, estimate this adjusted value, and then administer the transformer’s energization. To this end, a simple pre-fluxing device is introduced to adjust the remnant flux before transformer energization. Throughout flux adjustment, the remnant flux is estimated using appropriate formulas. The energization instant is determined based on the estimated remnant flux and circuit breaker operating characteristics. The proposed method is implemented in PSCAD/EMTDC and evaluated under a wide variety of conditions. Extensive simulations demonstrate the MPFM’s ability to accurately estimate the core’s adjusted remnant flux. The superiority of the MPFM over the conventional pre-fluxing method can be confirmed by comparing the reductions of the inrush current’s magnitude brought about by the two methods.